Howdy, I have one fully grown Tiger Oscar which I have had for years and for the past couple of weeks he/she (don't know how to tell if male or female) has become extremely territorial and will literally attack me while cleaning the tank/filter. I was just wondering if anyone can give me any info on why this is the case as he has never been like this before. Thanks

Can you be more specific in describing the fish and your tank setup? What size exactly are they both? How many years exactly have you had them? Does the oscar live alone or have companions? Were there any changes in the past few weeks?_________________Success with a fish/tank is measured in YEARS, not months or weeks...

OK let's see...that's about 90x60x60 cm ~ 320 liters. Good enough for an adult oscar and 2 sailfin plecos, although the oscar would probably enjoy a longer tank.

Large, intelligent cichlids such as oscars are known to develop behaviors like you described, especially when they're kept alone--as in no other intelligent cichlids to interact with (pleco behavior is completely alien to them).

If you read the Gallery section on Oscars, Red Devils, Texas, Doviis, and so on you'll see lots of reports such as yours. They're known to do worse and destroy heaters or anything else inside the tank, splash water on unsuspecting visitors, and all sorts of other "misbehaviors". Think of them as underwater dogs...if they don't have their own kind to display their natural behaviors, you become the only one they can interact with...

The parallel with dogs goes even further...many people find that they can help cure an oscar's boredom/loneliness by giving it some toys to fool around with...plastic balls are a classic example. Obviously, these should be small enough to hold with their mouths, but big enough that they won't accidentally swallow._________________Success with a fish/tank is measured in YEARS, not months or weeks...